Electric field sensor

Abstract

An electric field sensor which measures an electric field generated by a target utilizing an electro-optic effect, the electric field sensor including a light source, an electro-optic crystal on which light in a predetermined polarization state emitted from the light source is incident and which is subjected to the electric field generated by the target, a reference electric field applicator configured to apply an electric field based on a reference signal with a known signal level to the electro-optic crystal, a light receiver configured to receive light emitted from the electro-optic crystal and to convert the received light into an electric signal, and a separation corrector configured to separate the electric signal into a measurement signal based on the electric field generated by the target and the reference signal and to correct a signal level of the measurement signal on the basis of the signal level of the separated reference signal.

The invention claimed is: 
     
       1. An electric field sensor which measures an electric field generated by a target utilizing an electro-optic effect, the electric field sensor comprising:
 a light source; 
 an electro-optic crystal on which light in a predetermined polarization state emitted from the light source is incident and which is subjected to the electric field generated by the target; 
 a reference electric field applicator configured to apply an electric field based on a reference signal with a known signal level to the electro-optic crystal; 
 a light receiver configured to receive light emitted from the electro-optic crystal and to convert the received light into an electric signal; and 
 a separation corrector configured to separate the electric signal into a measurement signal based on the electric field generated by the target and the reference signal and to correct a signal level of the measurement signal on the basis of the signal level of the separated reference signal, 
 wherein the light receiver comprises: 
 a polarization beam splitter configured to separate circularly polarized light emitted from the electro-optic crystal into P-polarized light and S-polarized light; and 
 a differential amplifier configured to amplify a differential component of electric signals of the P-polarized light and the S-polarized light separated by the polarization beam splitter and to output the amplified electric signal to the separation corrector, and 
 wherein the separation corrector comprises: 
 a filter configured to remove a signal component of the electric field based on the reference signal in the electric signal output from the differential amplifier; 
 an amplifier configured to extract a signal component of the electric field based on the reference signal in the electric signal output from the differential amplifier using the reference signal; 
 a gain controller configured to generate a control signal that controls an amplification factor according to the signal component of the electric field based on the reference signal output from the amplifier; and 
 a variable gain amplifier configured to vary an amplification factor of the electric signal output from the filter in which the signal component of the electric field based on the reference signal is removed according to the control signal output from the gain controller, and to output the electric signal. 
 
     
     
       2. The electric field sensor according to  claim 1 , wherein the separation corrector comprises:
 a first separator configured to separate the measurement signal from the electric signal; 
 a second separator configured to separate the reference signal from the electric signal; and 
 a corrector configured to correct the signal level of the measurement signal on the basis of the signal level of the separated reference signal. 
 
     
     
       3. The electric field sensor according to  claim 1 , further comprising:
 a measurement electric field applicator configured to apply a referential signal with a known signal level to the target, 
 wherein the separation corrector comprises: 
 a first separator configured to separate the measurement signal, on which the referential signal is superimposed, from the electric signal; 
 a second separator configured to separate the reference signal from the electric signal; and 
 a corrector configured to correct the signal level of the measurement signal on the basis of the signal level of the separated reference signal. 
 
     
     
       4. The electric field sensor according to  claim 3 , wherein
 the target is a solar cell, 
 the light source is configured to irradiate the solar cell with light, and 
 the electro-optic crystal is subjected to an electric field generated by the solar cell irradiated with the light from the light source as the electric field generated by the target. 
 
     
     
       5. The electric field sensor according to  claim 1 , wherein the electro-optic crystal comprises:
 a first optical waveguide on which light of the light source is incident; 
 a first electrode which is connected to a first output of the first optical waveguide and to which the electric field generated by the target is input; 
 a second electrode which is connected to the first electrode and to which the electric field based on the reference signal is applied; 
 a third electrode which is connected to the first output of the first optical waveguide and grounded; and 
 a second optical waveguide having a first input to which the second electrode is connected, a second input to which the third electrode is connected, and an output connected to the light receiver. 
 
     
     
       6. The electric field sensor according to  claim 1 , wherein the predetermined polarization state is circularly polarized light. 
     
     
       7. The electric field sensor according to  claim 1 , wherein a frequency of the reference signal is in a frequency band that does not affect the measurement signal. 
     
     
       8. An electric field sensor which measures an electric field generated by a target utilizing an electro-optic effect, the electric field sensor comprising:
 a light source; 
 an electro-optic crystal on which light in a predetermined polarization state emitted from the light source is incident and which is subjected to the electric field generated by the target; 
 a reference electric field applicator configured to apply an electric field based on a reference signal with a known signal level to the electro-optic crystal; 
 a light receiver configured to receive light emitted from the electro-optic crystal and to convert the received light into an electric signal; 
 a separation corrector configured to separate the electric signal into a measurement signal based on the electric field generated by the target and the reference signal and to correct a signal level of the measurement signal on the basis of the signal level of the separated reference signal; and 
 a measurement electric field applicator configured to apply a referential signal with a known signal level to the target, 
 wherein the light receiver comprises: 
 a polarization beam splitter configured to separate circularly polarized light emitted from the electro-optic crystal into P-polarized light and S-polarized light; and 
 a differential amplifier configured to amplify a differential component of electric signals of the P-polarized light and the S-polarized light separated by the polarization beam splitter and to output the amplified electric signal to the separation corrector, and 
 wherein the separation corrector comprises: 
 a first amplifier configured to extract a signal component of an electric field based on the measurement signal in the electric signal output from the differential amplifier using the measurement signal; 
 a second amplifier configured to extract a signal component of an electric field based on the reference signal in the electric signal output from the differential amplifier using the reference signal; 
 a gain controller configured to generate a control signal that controls an amplification factor according to a signal component of the electric field based on the reference signal output from the second amplifier; and 
 a variable gain amplifier configured to vary an amplification factor of the electric signal of the signal component of the electric field based on the measurement signal output from the first amplifier according to the control signal output from the gain controller, and to output the electric signal. 
 
     
     
       9. An electric field sensor which measures an electric field generated by a target utilizing an electro-optic effect, the electric field sensor comprising:
 a light source; 
 an electro-optic crystal on which light in a predetermined polarization state emitted from the light source is incident and which is subjected to the electric field generated by the target; 
 a reference electric field applicator configured to apply an electric field based on a reference signal with a known signal level to the electro-optic crystal; 
 a light receiver configured to receive light emitted from the electro-optic crystal and to convert the received light into an electric signal; 
 a separation corrector configured to separate the electric signal into a measurement signal based on the electric field generated by the target and the reference signal and to correct a signal level of the measurement signal on the basis of the signal level of the separated reference signal; 
 a transparent electrode disposed on a first surface of the electro-optic crystal; and 
 a mirror disposed on a second surface of the electro-optic crystal facing the first surface, 
 wherein light emitted from the light source is incident from the transparent electrode, the light incident from the transparent electrode is reflected by the mirror, and the reflected light is emitted from the transparent electrode, 
 wherein the separation corrector is configured to measure the electric field generated by the target by acquiring a phase change of light that has been emitted by the light source, reflected by the mirror, and returned through the transparent electrode, 
 wherein the light receiver comprises: 
 a polarization beam splitter configured to separate circularly polarized light emitted from the electro-optic crystal into P-polarized light and S-polarized light; and 
 a differential amplifier configured to amplify a differential component of electric signals of the P-polarized light and the S-polarized light separated by the polarization beam splitter and to output the amplified electric signal to the separation corrector, and 
 wherein the separation corrector comprises: 
 a filter configured to remove a signal component of the electric field based on the reference signal in the electric signal output from the differential amplifier; 
 an amplifier configured to extract a signal component of the electric field based on the reference signal in the electric signal output from the differential amplifier using the reference signal; 
 a gain controller configured to generate a control signal that controls an amplification factor according to the signal component of the electric field based on the reference signal output from the amplifier; and 
 a variable gain amplifier configured to vary an amplification factor of the electric signal output from the filter in which the signal component of the electric field based on the reference signal is removed according to the control signal output from the gain controller, and to output the electric signal.